Post-operative knee rehabilitative dynamometer

ABSTRACT

Apparatus for measuring changes in human joint strength includes an open-cell body of flexible foam, an airtight flexible skin sealed about said foam body, with skin having an opening permitting passage of air into and out of the foam body, a hose sealed about the opening to channel air passing in and out of the opening through the hose and a gauge connected to the hose for measuring the force of air passing through the hose upon application of the force against the foam body.

This patent application is a continuation of U.S. Ser. No. 07/289,587,filed Dec. 22, 1988, now U.S. Pat. No. 4,943,053 issued Jul. 24, 1990.

FIELD OF THE INVENTION

This invention relates to apparatus for measuring changes in human jointstrength and particularly relates to apparatus for facilitating humanknee joint rehabilitation through exercise and measuring changes inhuman knee joint strength during post-operative knee rehabilitation.

BACKGROUND OF THE INVENTION

Surgery on the human knee or knee joint nearly always requiresrebuilding of muscular strength in the knee and/or in connective tissuesurrounding the knee. Various methods and apparatus have been designedto facilitate rehabilitation of knee function. These typically includeknee exercises designed to restore knee strength to previous or at leastacceptable levels.

Most afflictions of the knee joint are exacerbated by weak quadricepsand hamstring muscles as the patient begins to favor the painful joint.This many times initiates a vicious cycle of increased pain andincreased muscle weakness leading to progressive joint instability. Thequadriceps and hamstrings are the dynamic stabilizers of the knee jointand must be kept at maximum strength for optimal knee joint function.

Typical rehabilitative methods and programs extend over a period oftime, usually measured in months, to achieve the desired level ofrecaptured knee strength. Measurements of knee strength are periodicallytaken to determine progress or completion of the required rehabilitationregimen. It has, therefore, become necessary to provide apparatuscapable of measuring the relative restored knee joint strength todetermine when it is possible or desirable to discontinue joint musclestrength rehabilitation.

DESCRIPTION OF THE PRIOR ART

Prior art known to applicant includes U.S. Pat. Nos. 3,791,375;3,974,491; 4,286,603; 4,337,780; 4,521,186; and 4,592,371. Of these,'780 and '371 are believed to be the most relevant with respect to theinvention disclosed and claimed herein.

'780 discloses a muscle testing apparatus and technique wherein anairtight bag is connected to a pressure responsive device by flexibletubing. The airtight bag is provided with elastic bands for attachingthe bag and a pressure responsive gauge to the hand of the user. Asecond embodiment includes a small airtight bag, a large airtight bag, atwo way valve and a pressure responsive device, all connected byflexible tubing. The small airtight bag has elastic bands for attachmentto the palm side of one finger. The larger airtight bag has elasticbands for attachment to the palm of the user's hand. The user squeezesthe airtight bag which exerts pressure through the tubing, therebycausing a pressure reading to be displayed on the pressure responsivedevice/gauge.

'371 discloses a method and apparatus for muscle testing. An air bag isinflated by pumping air through a connecting hose by a flexible rubberbulb. A gauge attaches to the air bag by the flexible hose. To test thestrength of a muscle or a set of muscles, the patient first appliesforce to the air bag. After inflating the air bag via a bulb, theapplied force is measured by the gauge by the process being repeated.The gauge readings are compared to determine differences in musclestrength.

SUMMARY OF THE INVENTION

This invention encompasses apparatus for providing post-operativerehabilitation for a human knee joint through exercise and forsimultaneously measuring changes in human joint strength, including anopen-cell body of light weight, low density polyurethane foam and anairtight flexible skin about the foam body. The light weight low densitypolyurethane foam having the preferably air tight flexible skin aboutthe foam provides apparatus for the human to rehabilitate the knee jointthrough post-operative therapy by providing a controlled amount ofresistance to flexure and being of dimensions which are believed to beoptimal for the quadricep setting exercise (which is the cornerstone oftherapy for knee disorders and knee post-operative rehabilitation).

The compression permitted by the low density polyurethane form enhancesthe exercise value when the apparatus is used for therapy. The skinpreferably is dip molded elastomeric material and has at least oneopening to permit passage of air to and from the foam body. A hose issealed about the opening with a rubber seal. The hose is also connectedalong the length of the hose to the foam body, extending within the foambody. The hose preferably extends into a center portion of the foambody, remote from the opening, thereby channeling air passing in and outof the opening through the hose. A gauge attaches to the hose formeasuring the force of air passing through the hose upon application offorce against the foam body. The gauge connects to a rigid couplingmember, which connects to the hose.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic front elevational view of apparatus in accordancewith the invention.

FIG. 2 is a schematic front elevational view of a preferred embodimentof the invention, partially taken in section.

FIG. 3 is a schematic front elevation view of apparatus embodyingaspects of the invention in use.

DESCRIPTION OF THE PREFERRED EMBODIMENTS AND BEST MODE FOR PRACTICINGTHE INVENTION

Referring to the drawings in general and to FIGS. 1 and 2 in particular,apparatus for providing post-operative therapeutic exercise and forsimultaneously measuring changes in human joint strength duringpost-operative knee rehabilitation is designated generally 10. Apparatus10 includes pillow 12 consisting of a foam body portion 14 and an outerskin 16. Skin 15 contains an opening 18 which is capped by and sealed torubber grommet 20. Flexible tubing 22 extends inwardly into grommet 20through grommet opening 24. Flexible tubing 22 is preferably sealed bycement to the foam body portion 14 of pillow 12 along the entire lengthof flexible tubing 22 which is within foam body 14 of pillow 12. Inpractice, flexible tubing 22 preferably extends about 4 inches into thefoam body portion 14 and cement sealing of tubing 22 to foam bodyportion 14 is preferably provided along the entirety of the 4 inchtubing length which is within pillow 12.

The other end of flexible tubing 22 extends into bore 28 of a preferablyfoam grip member 30. A tubular coupling 32 is located within andsurround by foam grip 30. Coupling 32 receives flexible tubing 22 at itslower end 34 with tubing 22 extending through bore 28. Upper end 36 ofcoupling 32 receives gauge mount 38 from gauge 40. Gauge mount 38extends into and is received by the end of flexible tubing 22. Gauge 40contains passive pointer 42 and active pointer 44. A cloth sleeve (notshown) may be placed over or around pillow 12 for sanitary and/oraesthetic purposes.

Referring to FIG. 2, a preferred embodiment of apparatus 10 is shown.Skin 16 is preferably created by dip molding, with foam body portion 14being dipped into a suitable liquid phase elastomeric material so thatthe elastomeric material molds itself to the outer configuration of foambody portion 14. Foam body 14 consists of an open cell low densitypolyurethane.

Flexible tubing 22 extends into foam body 14, preferably to a middleportion of foam body 14. Although it is possible that flexible tubing 22not extend to the middle of foam body 14, such placement assists inobtaining more accurate and consistent gauge readings. Additionally,having flexible tubing extending into the foam body 14 and beingcemented along the length that flexible tubing extends into foam body 14provides more secure attachment of flexible tubing 22 to foam body 14.

Referring now to FIGS. 1 and 2 generally, foam body portion 14preferably consists of a generally cylindrically shaped piece ofopen-cell polyurethane foam. It is not necessary that any particularfoam be utilized, however, it is preferred that the foam have a firmnessrating of about 35-45 I.L.D. and a density of approximately 1.8 lbs/ft³.

Pillow 12 is preferably about 12 inches long to enable the full width ofthe joint to contact the apparatus. The diameter of pillow 12 is mostpreferably about 4.75 inches to achieve about a 30 degree jointinflection prior to application of downward force by the joint on pillow12. Skin layer 16 surrounding foam body 14 preferably is thin, mostpreferably having a thickness of between about 10 mls and about 22 mils.Pillow 12 is preferably formed having its edges, at either end of thecylinder, formed on 5/8 inch radii.

The elastomeric material used to form skin 16 may be PDC-10 (asmanufactured by PDI, Inc. of St. Paul, Minn.) consisting primarily of 1,1, 1-trichloromethane, methylene chloride, petroleum distillates andtoluene. PDC-10 has a low viscosity which enables it to easily fillpores and holes on the surface of foam body 14. This achieves theadditional benefit of increased mechanical bonding of the skin to thefoam body.

Skin 16 may, alternatively, be Flexabar brand vinyl material(manufactured by Flexabar Corp. of Northvale, N.J.) consisting primarilyof methyl ethyl ketone, methyl isobutyl ketone, toluol, red 2B pigment,dioctyl phthalate, isodecyl diphenyl phosphate and polyvinyl chloridecopolymer. Skin 16 is most preferably applied by dipping pillow 12, butmay be applied by other methods.

Flexible tubing 22 preferably consists of PVC tubing havingreinforcement of nylon braids. Flexible tubing 22 is preferablyconnected to pillow 12 using a flat, washer-shaped Neoprene bushing orgrommet. Foam grip member 30 preferably consists of a smooth bore sleeveof dip molded vinyl foam. Coupling 32, residing within foam grip member30, preferably consists of a hollow wood dowel and connects to gauge 40by gauge mount 38.

Gauge 40 preferably a brass diaphragm, contains an all brass gearmovement and a brass pressure inlet with a restriction orifice. Thegauge may have a scale range of about 0 to 100 inches of water orwhatever scale range is desired for a particular application.

Referring now to FIG. 3, apparatus 10 facilitates rehabilitativeexercise of the human knee joint and provides improved measurement ofchanges in human joint strength during and resulting from rehabilitationof the joint. The most common joint for rehabilitation knee joint and itis the knee joint to which the invention is principally directed,although it is well within the scope of the invention to employapparatus 10 in rehabilitation of other joints, such as the elbow, forexample.

It is preferred to place apparatus 10 on a flat surface designated 54 inFIG. 3. The joint to be rehabilitated is then placed over the surface offoam body 12 opposing that in contact with flat surface 54. Thepreferred angle of joint flex is about 30°. The patient then grasps foamgrip 32 with his or her hand 56 to facilitate reading pointers 42 and 44on gauge 40.

The patient then applies downward force, in the direction shown by arrowA, using the joint being rehabilitated, to foam body 12. Application ofdownward force by the knee joint provides therapeutic exercise andrehabilitation for the knee joint. The subject can apply such downwardforce as many times as the subject likes or as prescribed by theattending physician or other health professional. Hence, apparatus 10provides mechanical means of performing the rehabilitative exercise aswell as means of measurement of the change in strength of the joint andassociated supportive and connective tissue. The dimensions of theapparatus, set forth above, particularly the diameter of about four andthree quarter inches, have been found to be optimal for the quadricepsetting exercise, which is the cornerstone of therapy for knee disordersand post-operative knee rehabilitation.

Application of downward force on foam body 12 from above (by the joint)and simultaneous resistance to downward movement along surface 54 causescompression force in foam body 12, thereby compressing foam body 12. Aircontained within the open cell structure of foam 14 is forced outwardlyand exits foam body 12 by way of flexible tube 22. Exiting air thentravels there through to gauge 40. The resulting air pressure withingauge 40 causes active pointer 42 to move along the face of gauge 40 toproduce a reading.

Release of downward force by the joint releases compressive force onfoam body 12, thereby releasing air pressure within gauge 40, coupling32 and flexible tubing 32. Foam body 12 then returns to its originaluncompressed state and volume. Repeated compression and decompression offoam body 12 enables utilization of passive pointer 44 to indicate amaximum amount of compressive force, thereby indicating maximum jointstrength achievable during that rehabilitation session.

The above procedure may be performed repeatedly during the samerehabilitation session to obtain a range of measurements, and/or may berepeated periodically to determine changes in joint strength over time.The device, by providing both therapeutic exercise and rehabilitativetherapy for the knee joint and permitting the physician or other healthprofessional to monitor the patient's progress during rehabilitation,enhances the physician's or other physical therapist's ability toeffectively rehabilitate the injured joint.

I claim:
 1. Apparatus for measuring strength of joint-operating musclesin humans comprising:a. an axially elongated open-cell cylindrical bodyof which is sufficiently flexible to be radially compressed yetsufficiently rigid to maintain its cylindrical shape when uncompressed;b. an airtight flexible skin sealed about said foam body, said skinhaving an opening to permit passage of air in to and out of said foambody; c. a hose sealed about said opening for passage of air in and outof said foam body through said opening and said hose; d. means connectedto said hose for measuring pressure of air within said body and saidhose upon external application of compressive force to said foam body.2. Apparatus as defined in claim 1 wherein said hose extends into acenter portion of said foam body.
 3. Apparatus as defined in claim 1further comprising a rubber grommet positioned around said hose andsealed at said opening to provide an airtight seal.
 4. Apparatus asdefined in claim 1 where in said means to measure force comprises agauge.
 5. Apparatus as defined in claim 4, wherein said gauge connectsto one end of a coupling member, said coupling member having a barbedfitting on the other end to connect to said hose.
 6. Apparatus asdefined in claim 5, wherein said coupling member is surrounded by aflexible foam hand grip.
 7. Apparatus as defined in claim 1, whereinsaid foam body comprises light weight, low density polyurethane foam. 8.Apparatus as defined in claim 1, wherein said skin about 10 to 22 milsin thickness.
 9. Apparatus as defined in claim 1, wherein said foam bodyhas a density of about 1.8 lbs./ft.³.
 10. Apparatus for measuringchanges in human joint strength comprising:a. an axially elongatedopen-cell cylindrical body, having diameter such that when positionedunder a subject's knee between a floor and the subject's substantiallyhorizontally extended knee, the subject's associated hip and anklecontinue to contact said floor, of light weight, low densitypolyurethane foam which is sufficiently flexible to be radiallycompressed yet sufficiently rigid to maintain its cylindrical shape whenuncompressed; b. an airtight flexible skin sealed about said foam body,said skin comprising a multi-layer vinyl material and having an openingto permit passage of air in to and out of said foam body; c. a hosesealed about said opening with a rubber seal, one end of said hoseextending into a center portion of said foam body remote from saidopening, said hose channeling air passing in and out of said opening; d.means connected to said hose for measuring the force of air passagethrough said hose upon application of force against said foam body,comprising a coupling member connected to said hose on one end and agauge connected to the other end of said coupling member.
 11. Apost-operative knee rehabilitative dynamometer comprising:a. an axiallyelongated cylindrically shaped open-cell body having diameter such thatwhen positioned under a subject's knee between a floor and the subject'ssubstantially horizontally extended knee, the subject's associated hipand ankle continue to contact said floor of light weight, low densitypolyurethane foam body which is sufficiently flexible to be radiallycompressed yet sufficiently rigid to maintain its cylindrical shape whenuncompressed; b. an airtight, flexible skin having a thickness of about10 to about 22 mils sealed about said foam body, said skin comprising atleast one layer of vinyl material containing rubber based balloons as athickening agent, at least one layer of vinyl based paint and a glosscoat layer, said skin having an opening to permit passage of air intoand out of said foam body; c. a hose sealed about said opening with arubber grommet and extending into the center of said foam body remotefrom said opening, said hose channeling air passing in an out of saidopening; d. means connected to said hose for measuring the force of airpassing through said hose upon application of knee force against saidfoam body, comprising a gauge having an active and passive markerconnected to one ned of a coupling member, said coupling member beingsurrounded by a flexible foam hand grip and connected to said hose onits other end.